FIG. 1 shows a block diagram of a conventional system 100 for balancing multiple battery cells 101-1 through 101-n. The cell balancing system 100 includes multiple bypass paths 110-1 through 110-n, multiple analog-to-digital (A/D) converters 120-1 through 120-n, and a central control block 130. Each bypass path coupled to a corresponding battery cell includes a resistor and a switch. The A/D converters 120-1 through 120-n are coupled to the battery cells 101-1 through 101-n, respectively. For example, a bypass path 110-i coupled to a battery cell 101-i includes a resistor 112-i and a switch 114-i. An A/D converter 120-i is coupled to the battery cell 101-i. 
In operation, the A/D converter 120-i converts a cell voltage Vcelli of the battery cell 101-i into a digital signal and transmits the digital signal to the central control block 130. The central control block 130 receives digital signals representative of cell voltages Vcell1-Vcelln of the battery cells 101-1 through 101-n to determine if there is any battery cell undergoing an unbalanced condition. For example, a battery cell is detected as an unbalanced battery cell if a cell voltage difference between the detected battery cell and another battery cell is greater than a predetermined threshold. The central control block 130 switches on a switch in a bypass path coupled in parallel with the unbalanced battery cell to enable a bypass current for the unbalanced battery cell. However, the A/D converters 120-1 through 120-n are relatively expensive. As a result, the cost of the system 100 is relatively high.